Question

A racing car moving towards a cliff sound its horn. The driver observes that the sound reflected from the cliff has a pitch one octave higher than the actual sound of the horn. If v is the velocity of sound, the velocity of the car is?

(a) v/√2

(b) v/2

(c) v/3

(d) v/4

I had been asked this question in an interview.

This question is from Stationary Waves topic in portion Waves of Engineering Physics I

Answer 1

Right choice is (c) v/3

Easiest explanation: γ^‘/γ=(v+vs)/(v-vs)=2

v+vs=2v-2vs

3vs=v or vs=v/3.